Study Of Paulownia Growth And Physiological Under Different Levels Of Light And Water

Paulownia is one of the main Fast-growing timber species with some characteristics of fast-growing, wide adaptability and breeding easily in China. The article analysis the differences of seeding-stage Paulownia’s growth indicators, biochemical indexes and photosynthetic physiological indexes under different levels of light and water. There was 4 levels of water:75-80%,55-60%,40-45%,25-30%, and 3levels of light: No-shading condition (100%NS),a layer of shade(23.6%NS) and two layers of shade(5.7%NS). Results:(1) When seeding-stage Paulownia was under the Low-light and drought stress, the amount of height and basic diameter were decreased significantly. The correlation between them was highly significant.(2) Under a layer and two layers of shading, severe drought stress increased MDA content significantly. Under the no-shading condition, when normal water and severe drought, the MDA content significantly higher than that of mild and moderate drought. Under the normal water and severe drought, shade decreased the MDA content to some content, the MDA content under a layer of shade was lower significantly than that of no-shading and two layers of shade. To some content, drought stress result the free Proline content increased, but severe drought result it decreased significantly. Soluble sugar content was increased with drought stress degree increasing. Different degrees of water treatment result in different effects on soluble protein under different layers of shade condition. Low-light stress result the content of free Proline, soluble sugar and protein decreased significantly. Shading treatment result in the decreasing of SOD, CAT activity significantly and the increasing of POD activity significantly. Different degrees of water treatment result in different effects on SOD, CAT, POD under different layers of shade.(3) Low-light stress result the photosynthetic pigment content increased and the severe drought stress decreased it significantly. It was positively correlated between Pn, Gs and Tr, but they were negatively correlated with Ci. Drought stress result that the curve of diurnal change of Pn, Tr were from single-peak type to double-peak type under no-shading condition and teo layers of shade, Ci diurnal variation curve from "V" to "W". Under a layer of shade condition, the curve of diurnal change of Pn, Tr and Gs were all single-peak type, the curve of diurnal change of Ci were "V" type. Under no-shading and a layer of shade condition, a, LSP, Pnmax and Rd decreased with the decreasing of water degree, but severe drought stress result the LCP decreased significantly. Except a, the other parameters of light response curve were decreasing under shade conditions.(4) Connectively analysis showed that the seeding-stage Paulownia growed slowly, the content of MDA, protective enzymes and osmoticas content rised with it under the light and miderate drought stress. The severe drought stress made it in very low rate of growth, and MDA content was highly increased, protective enzymes activity and osmoticas content was decreased greatly. Drught stress made the photosynthesis efficiency went down. Under a layer of shading condition, the harmful effect from drought stress was remetitent. We could know it by the evidence that the protective enzymes activity went up and the MDA content went down, in addition, the midday depression was disappeared. Under two layers of shading condition, the seeding-stage Paulownia’s growth rate decreased severesly, protective enzymes activity lower than no-shanding condition, MDA content was increased and photosynthesis efficiency significantly reducted.As a result, appratiate shading treatment could increase the resistance of the seeding-stage Paulownia to drought stress.